全文获取类型
收费全文 | 7812篇 |
免费 | 14篇 |
国内免费 | 16篇 |
专业分类
航空 | 3733篇 |
航天技术 | 2581篇 |
综合类 | 23篇 |
航天 | 1505篇 |
出版年
2021年 | 57篇 |
2018年 | 222篇 |
2017年 | 168篇 |
2016年 | 115篇 |
2015年 | 60篇 |
2014年 | 172篇 |
2013年 | 200篇 |
2012年 | 219篇 |
2011年 | 370篇 |
2010年 | 275篇 |
2009年 | 401篇 |
2008年 | 454篇 |
2007年 | 281篇 |
2006年 | 168篇 |
2005年 | 244篇 |
2004年 | 205篇 |
2003年 | 240篇 |
2002年 | 141篇 |
2001年 | 243篇 |
2000年 | 114篇 |
1999年 | 159篇 |
1998年 | 192篇 |
1997年 | 139篇 |
1996年 | 148篇 |
1995年 | 209篇 |
1994年 | 215篇 |
1993年 | 119篇 |
1992年 | 148篇 |
1991年 | 78篇 |
1990年 | 72篇 |
1989年 | 138篇 |
1988年 | 66篇 |
1987年 | 65篇 |
1986年 | 72篇 |
1985年 | 192篇 |
1984年 | 179篇 |
1983年 | 149篇 |
1982年 | 148篇 |
1981年 | 239篇 |
1980年 | 68篇 |
1979年 | 63篇 |
1978年 | 63篇 |
1977年 | 52篇 |
1976年 | 54篇 |
1975年 | 53篇 |
1974年 | 50篇 |
1973年 | 49篇 |
1972年 | 59篇 |
1971年 | 40篇 |
1970年 | 40篇 |
排序方式: 共有7842条查询结果,搜索用时 46 毫秒
701.
Security applications of computer vision 总被引:1,自引:0,他引:1
In an age which bears witness to a proliferation of Closed Circuit Television (CCTV) cameras for security and surveillance monitoring, the use of image processing and computer vision techniques which were provided as top end bespoke solutions can now be realised using desktop PC processing. Commercial Video Motion Detection (VMD) and Intelligent Scene Monitoring (ISM) systems are becoming increasingly sophisticated, aided, in no small way, by a technology transfer from previously exclusively military research sectors. Image processing is traditionally concerned with pre-processing operations such as Fourier filtering, edge detection and morphological operations. Computer vision extends the image processing paradigm to include understanding of scene content, tracking and object classification. Examples of computer vision applications include Automatic Number Plate Recognition (ANPR), people and vehicle tracking, crowd analysis and model based vision. Often image processing and computer vision techniques are developed with highly specific applications in mind and the goal of a more global understanding computer vision system remains, at least for now, outside the bounds of present technology. This paper will review some of the most recent developments in computer vision and image processing for challenging outdoor perimeter security applications. It also describes the efforts of development teams to integrate some of these advanced ideas into coherent prototype development systems 相似文献
702.
703.
The basic principles of selecting some design parameters of a lightweight airplane for the contemporary Russian market are presented. Recommendations for selecting these parameters with the service requirements specified are given based on the study performed. 相似文献
704.
Flutter and time errors are critical factors in all instrumentation recording. This paper presents analytically the relationship between flutter, time base error, and time base error difference (sometimes called jitter), and the effects of these factors on direct and FM recording. Methods of measuring these quantities are discussed and experimental examples are given. Finally, a measurement method for the interchannel time error is presented, and some trends of correlation among all channels are discussed. 相似文献
705.
到过法国的旅游者,一般都知道巴黎有两个著名的歌舞表演厅,—个是位于市中心香榭丽舍大道的丽都,一个是位于城北蒙马特高地脚下白色广场附近的红磨坊。屋顶上装着长长的、闪烁着红光的大叶轮的红磨坊则是较为地道的法国式歌舞厅。MCG公司以法国红磨坊红磨坊为设计理念,把次情景带进了香港兰桂坊酒店Bisous酒吧。然而Bisous的设计并非照搬红色的浪漫风情,而是将未来趋势的一种极简概念设计结合了新的元素,将红磨坊的主题得以抽象化和现代化。以现今最时新的手法,完整地呈现了"红磨坊"的内心世界,概念可能不算创新,但精彩程度符合了当下时尚的思想! 相似文献
706.
P Rettberg G Horneck 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2000,26(12):2005-2014
Biological dosimetry has provided experimental proof of the high sensitivity of the biologically effective UVB doses to changes in atmospheric ozone and has thereby confirmed the predictions from model calculations. The biological UV dosimeter 'biofilm' whose sensitivity is based on dried spores of B. subtilis as UV target weights the incident UV radiation according to its DNA damaging potential. Biofilm dosimetry was applicated in space experiments as well as in use in remote areas on Earth. Examples are long-term UV measurements in Antarctica, measurements of diurnal UV profiles parallel in time at different locations in Europe, continuous UV measurements in the frame of the German UV measurement network and personal UV dosimetry. In space biofilms were used to determine the biological efficiency of the extraterrestrial solar UV, to simulate the effects of decreasing ozone concentrations and to determine the interaction of UVB and vitamin D production of cosmonauts in the MIR station. 相似文献
707.
The Monitor-E spacecraft executed uncontrolled flight due to emergency situation, no telemetry information on parameters of the spacecraft’s
attitude motion being available. So, the problem arose to determine the spacecraft’s rotational motion from the accessible
indirect information—the electric current provided by solar batteries. In this paper the integrated statistical technique
is described, that allows one to solve this problem. The values of current, obtained over the time interval some tens of minutes
long, have been processed simultaneously by the least squares method using the integration of the equations of spacecraft’s
rotational motion. As a result of processing, the initial conditions of motion were estimated, and the spacecraft’s moments
of inertia were updated, as well as the angles, specifying solar batteries position in the spacecraft-fixed coordinate system.
The results of processing of 12 data sets are presented, which allowed us to reconstruct the actual rotational motion of the
spacecraft. 相似文献
708.
Purpose of the work is to analyze and to summarize the data of investigations into human hemodynamics performed over 20 years aboard orbital stations Salyut-7 and Mir with participation of 26 cosmonauts on space flights (SF) from 8 to 438 days in duration. The ultrasonic techniques and occlusive plethysmography demonstrated dynamics of changes in the cardiovascular system during SF of various durations. The parameters of general hemodynamics, the pumping function of the heart and arterial circulation in the brain remained stable in all the space flights; however, there were alterations in peripheral circulation associated with blood redistribution and hypovolemie in microgravity. The anti-gravity distribution of the vascular tone decayed gradually as unneeded. The most considerable changes were observed in leg vessels, equally in arteries (decrease in resistance) and veins (increase in maximum capacity). The lower body negative pressure test (LBNP) revealed deterioration of the gravity-dependent reactions that changed for the worse as SF duration extended. The cardiovascular deconditioning showed itself as loss of descent acceleration tolerance and orthostatic instability in the postflight period. 相似文献
709.
710.
Peebles Peyton Z. Berkowitz R. S. 《IEEE transactions on aerospace and electronic systems》1968,(6):845-854
The problem of determining target parameters of a known number of radar targets falling in the same range-Doppler-angle-angle resolution cell is examined for the noise-free case. The required minimum number of radar beams is determined, based upon approximating the beam patterns by a Taylor series expansion, both for the general problem and for factorable beams. Signal processors for target position estimation are developed for the two-target case and equations are presented for the general case. 相似文献